So i should be able change to alloys w/out letting insurance know about it,right?Wouldn't count as a modification...
So long as you fit a set of original Honda wheels. Anything fancy, and the insurance won't like it if it gets pinched.
Rattle at idle, you need to have a good listen to see where it's coming from. Could be something loose, as suggested above.
Steering not the lightest on the Jazz anyway, but does it feel like an intermittent problem? Tracking will make the steering twitchy with excessive toe out. When does it feel unstable, during any particular manoeuvre? Tyre pressures okay? Maybe get the shock absorbers checked at that age.